KITTANNING — A ruptured major vein in the stomach killed a 39-year-old Butler County man injured during a weekend fight in the borough, authorities said. Investigators, meanwhile, are seeking witnesses who were present at the early Sunday morning fight on Montieth Street that ended in the death of James P. Sullivan of Donegal Township. “We know there were a significant number of people there and they may have may have seen what happened,” said Armstrong County District Attorney Scott Andreassi. “We’d like to talk to them.” State police have already interviewed 10 or so people who were present about 1:35 a.m. when Sullivan and another man got into a physical altercation. “But we think there are more people with more information,” Andreassi said. Police believe they have identified the other man who fought with Sullivan but would not disclose his name.